The invention relates to novel chiral derivatives of Hibiscus acid bearing lactone ring moiety and the process for preparing the same.
Hibiscus acid [(+)-Hydroxycitric acid lactone or (2S,3R)-Tetrahydro-3-hydroxy-5-oxo-2,3-furandicarboxylic acid] can be isolated from the leaves/fruit calyxes of Hibiscus sabdariffa or from the leaves of Hibiscus furcatus, and Hibiscus cannabinus. Garcinia acid [(xe2x88x92)-Hydroxycitric acid lactone or (2S,3S)-Tetrahydro-3-hydroxy-5-oxo-2,3-furandicarboxylic acid,], a diastereomer of Hibiscus acid is widely used as an important ingredient in many pharmaceutical formulations1-10. 
The non-availability of Hibiscus acid in the market, in the optically pure form, has resulted in the limited use of Hibiscus acid or its derivatives in the broad area of organic synthesis and pharmaceutical front. This is due to the lack of any commercially viable large-scale manufacturing process. In U.S. patent application Ser. No. 09/365,300 an economic, commercially viable, cost effective process for the large-scale isolation of Hibiscus acid has been described11.
Also during the past two decades there has been a great deal of interest to find cheap and potential chiral molecules from chiral pool to accomplish synthetic pathways with a high degree of asymmetric induction12-25. 
Added to this, substituted xcex3-butyrolactones are known to be potent antagonists or agonists depending upon the substitution pattern of the xcex3-aminobutyric acid receptor, the major inhibitory neurotransmitter in the mammalian central nervous system26.
The known methods for obtaining diversity functionalised chiral xcex3-lactones are either by the cyclisation of acyclic starting materials such as the sterioselective iodolactonisation of unsaturated 3-hydroxy acids27 or from sugars such as D-ribofuranose or D-glucosamine or carbohydrates such as D-ribose, D-glucose etc28. These chemical modifications involving carbohydrates require tedious protocols.
Existing Methods:
a. The method reported by Per. M. Boll, Else Sorensen and Eric Balieu29 for the isolation of Hibiscus acid is from the calyxes of the fruits of Hibiscus sabdariffa. In this method dried, ground fruit calyxes of Hibiscus sabdariffia is extracted at room temperature for 68 hours several times with methanol containing 1.5% hydrogen chloride. To the pooled methanol extracts, ether is added and the coloring matter is deposited as a dark red syrupy mass. The ether layer is collected and syrup is dissolved in methanolic hydrogen chloride (1%) and again precipitated by the addition of ether. The pooled ether extracts is evaporated and the residue is dissolved in methanol. Upon cooling colorless crystals is obtained and the same is recrystallised from propanol and which was later hydrolysed to get Hibiscus acid.
b. Another method for the laboratory-scale production of Hibiscus acid described by C. Martius and R. Maue30, is purely a synthetic one. In this method Hibiscus acid is prepared from a number of chemical constituents and not from any natural source.
c. The method described by this author and co-workers is a general method for the isolation of Hibiscus acid in the optically pure crystalline form from the fresh or dried leaves and/or calyxes of Hibiscus sabdariffa and leaves of Hibiscus furcatus or Hibiscus cannabinus employ mostly organic solvents. The main extraction is done with acidic methanol, followed out by the removal of organic impurities by adding water. The resulting filtrate was further extracted with organic solvents to get crude Hibiscus acid, which was later purified by esterification followed by hydrolysis.
The Drawbacks of the Existing Method xe2x80x9caxe2x80x9d are:
1. The method fails to get pure Ia when leaves of the plants is used and is applicable only in the case of the fruit calyxes of Hibiscus sabdariffa. 
2. Hibiscus sabdariffa is a seasonal flowering plant and hence the calyxes is not available at any given time.
3. Large quantities of expensive solvent ether is required for the process.
4. Crystallisation was effected only on prolonged (2 months) storage over drierite, in a desiccater.
Method xe2x80x9cbxe2x80x9d describes the synthesis of formula Ia from chemical constituents and is not economically viable.
None of the existing methods (aandb) describes the complete characterization and degree of purity of the compound.
Method xe2x80x9ccxe2x80x9d describes basically the extraction with undesirable methanol and expensive diethyl ether as solvents.
The object of the present invention therefore is to prepare chial derivatives bearing lactone ring moiety and to provide a new method obviating the drawbacks of the existing methods.
To achieve the objectives, this invention provides novel chiral derivatives of Hibiscus acid bearing lactone ring moiety of formula I 
Wherein:
R1xe2x95x90R2xe2x95x90alkali salt of carboxylic acid or acid chloride or lower esters or the N-substituted cyclic imides.
R3xe2x95x90hydroxyl or protected hydroxyl group
In the above formula I
R1 and R2 is selected from
xe2x80x94COONa, xe2x80x94COCI, xe2x80x94COOCH2C6H5, xe2x80x94COOC2H5,

R2 is xe2x80x94OH or protected hydroxyl group to form various chiral derivatives of Hibiscus acid bearing lactone ring moiety.
Chiral Derivatives of Hibiscus Acid Bearing Lactone Ring Moiety:
Summary of the Chiral Derivatives of Hibiscus Acid Bearing Lactone Ring Moiety is Given Below in Scheme I: 
Compound of formula Ib is Disodium (2S,3R)-tetrahydro-3-hydroxy-5-oxo-2,3-furandicarboxylate
Compound of formula Ic is (2S,3R)-Tetrahydro-3-hydroxy-5-oxo-2,3-furandicarbonylchloride
Compound of formula Id is Dimethyl (2S,3R)-tetrahydro-3-oxo-[(methylthio)methoxy]-5-oxo-2,3-furandicarboxylate
Compound of formula Ie is (phenylmethyl)(2S,3R)-tetrahydro-3-hydroxy-5-oxo-2,3 furandicarboxylate
Compound of formula Ig is Diethyl (2S,3R)-tetrahydro-3-hydroxy-5-oxo-2,3-furandicarboxylate.
Compound of formula Ih is s Diisopropyl (2S,3R)-tetrahydro-3-hydroxy-5-oxo-2,3-furandicarboxylate.
Compound of formula Ij is (3aR,6aS)-3a-(acetyloxy)dihydro-5-(4-methoxy-phenyl methyl)-6H-furo[2,3-c]pyrrole-2,4,6(3H,4H)-trione
The present invention further provides a process of isolation of compound of Formula Ia, comprising:
extracting the Calyxes/leaves of Hibiscus sabdariffa, leaves of Hibiscus furcatus and Hibiscus cannabinus using water (X),
washing the extract (X) with organic solvent to remove impurities,
concentrating the aqueous layer,
adding an organic solvent to remove insoluble impurities,
evaporating the organic layer,
adding aqueous alkali to the concentrate to yield the alkali salt,
purifying the alkali salt by the addition of alcohol,
readjusting the pH by the addition of mineral acid,
concentrating and extracting the solution with organic solvents,
further concentrating the solution to get a syrup,
extracting the said syrup with solvents,
concentrating the obtained solution to get pure Ia in crystalline form.
The organic solvent used for washing is hexane.
The organic solvent used for removing impurities is selected from methanol or acetone.
The invention further includes a process for preparing the chiral derivative of Hibiscus acid of formula Ib comprising:
treating the aqueous solution of Ia with aqueous solution of alkali till the pH of the solution is neutral,
evaporating the resultant solution to dryness,
washing the residue with water miscible organic solvent,
drying the product Ib under vacuum.
The said alkali is sodium bicarbonate.
The invention further includes a process for preparing the chiral derivative of formula Ic comprising:
adding an organic halide to a suspension of Ib in organic solvent,
stirring the mixture for 1-4 hours, filtering the said mixture,
evaporating the said solution to get Ic as a hygroscopic solid.
The said organic solvent is ether.
The said organic halide is thionyl chloride.
The invention also includes a process for preparing the chiral derivative of Formula Id comprising:
adding DMSO, an organic acid and an anhydride to If,
allowing the mixture to stand for 34 days,
adding the reaction mixture to cold saturated aqueous solution of alkali,
stirring the mixture for 14 hours,
extracting the resultant solution with an organic solvent,
washing the extract with aqueous alkali,
drying the organic layer,
evaporating to get crude Id,
purifying the crude Id by chromatography to get pure Id as an yellow oil.
The said organic acid is acetic acid.
The said anhydride is acetic anhydride.
The said alkali is sodium bicarbonate.
The said organic solvent used for extraction is chloroform.
The invention further includes a process for preparing the chiral derivative of formula Ie wherein, comprising:
refluxing Ia with an appropriate alcohol and organic acid in toluene for 10-20 hours using Dean-Stark set up,
washing the mixture with aqueous alkali solution,
evaporating the organic phase,
recrystallising from organic solvents or their appropriate mixtures yielding Ie as a solid.
The said appropriate alcohol is benzyl alcohol.
The said anhydride is acetic anhydride.
The said alkali is sodium bicarbonate.
The said organic solvent used for crystallization is selected from hexane or ether.
The invention further includes a process for preparing the chiral derivative of formula Ig comprising:
adding organic halide to a suspension of Ib in absolute alcohol,
stirring the mixture for 24 hours,
neutralizing the mixture with aqueous alkali solution,
extracting the said mixture using organic solvent,
evaporating the mixture furnishing Ig as a yellow oil.
The said organic halide is thionyl chloride.
The said alcohol is ethanol.
The said alkali is sodium bicarbonate.
The said organic solvent is chloroform.
The invention further includes a process for preparing the chiral derivative of formula Ih comprising:
adding an organic halide to a suspension of Ib in appropriate dry alcohol,
stirring the mixture for 36 hours,
neutralizing with aqueous alkali solution,
extracting the said solution with an organic solvent.
evaporating and extracting using an appropriate organic solvent yielding Ih as a yellow oil.
The said organic halide is thionyl chloride.
The said appropriate alcohol is isopropyl alcohol.
The said appropriate alkali is sodium bicarbonate.
The said appropriate organic solvent is chloroform.
The organic solvent used after evaporation is hexane.
The invention further includes a process for preparing the chiral derivative of formulae Ij or Ik comprising:
refluxing the suspension of Ia in an organic halide for 3 hours,
concentrating the said mixture under vacuum,
dissolving the solid obtained in an organic solvent,
adding an appropriate amine to the dissolved solution,
stirring the mixture at room temperature for 4-18 hours
concentrating the solution under vacuum,
adding the organic halide to the semi-solid obtained
refluxing for 18 hours,
extracting with suitable organic solvent
subjecting the said extract to chromatography furnishing Ij or Ik as white crystals.
The said organic halide is acetyl chloride.
The said appropriate amine is 4-methoxy benzyl amine.
The said organic solvent is chloroform.
The process will now be described with reference to the foregoing examples.